The natural crystalline lens of the eye plays a primary role in focusing light onto the retina for proper vision. However, the natural lens at times is replaced with an artificial lens to make a refractive correction or because of damage or injury to the natural lens. Under these circumstances, the natural lens is surgically removed from the eye.
Surgical procedures which require only a small incision to be made in the eye have been developed for removing the natural lens. In accordance with these procedures, a slender cutting tip of a surgical instrument is inserted through the incision to emulsify the natural lens--typically through the use of ultrasonic vibrations. A sleeve surrounds the tip to shield the corneal tissue from the action of the tip, and define an annular conduit for the passage of a fluid which acts to cool the tip and irrigate the eye. The free end of the cutting tip, however, still projects beyond the sleeve to engage and emulsify the natural lens. Great care must therefore be taken by the surgeon to ensure that only the lens is engaged by the tip so that injury is avoided. The emulsified portions of the lens are aspirated from the eye through a central bore in the tip.
Further, during an operation, the surgical instrument is manipulated to remove the entire lens. On account of this movement, the sleeve can at times become pinched between the tip and the corneal tissue of the eye. The frictional contact between the sleeve and the vibrating tip can generate a significant amount of heat at the surgical site. The corneal tissue can be damaged by the heat in a matter of a few seconds.